The curtain air bags are mounted in the front and rear window pillars, and the roof edge along both sides.
When the air bag crash sensors detect a side impact of greater than moderate force, the curtain air bag inflates quickly and helps to reduce injury mainly to the rear outboard passenger's head caused by directly hitting interior parts such as a door or window. For more details about air bag deployment, refer to "SRS Air Bag Deployment Criteria".
In a side impact:
Greater than moderate impact to one side of the vehicle will cause the curtain air bag on that side only to inflate.

(With Front Passenger Occupant Classification System) In a roll-over:
In response to a vehicle roll-over, both curtain air bags inflate.

Warning Light/Beep
A system malfunction or operation conditions are indicated by a warning.Refer to Warning/Indicator Lights. Refer to Warning Sound is Activated.
Side Air Bags
SRS Air Bag Deployment CriteriaMazda 6 Owners Manual: Constant Monitoring
The following components of the air bag systems are monitored by a diagnostic
system:
Crash sensors, and diagnostic module (SAS unit),
Front air bag sensors
Air bag modules
Side crash sensors
Air bag/Front seat belt pretensioner system warning light
Front seat belt pretensioners
Re ...
Mazda 6 Owners Manual: Steering gear and linkage removal/installation
Caution
Performing the following procedures without first removing the ABS
wheel-speed sensor may possibly cause an open circuit in the harness if it
is pulled by mistake. Before performing the following procedures, remove the
ABS wheel-speed sensor (axle side) and fix it to an appropri ...